a_0,a_1,a_2 = [int(i) for i in input().split()]
r = (a_1-a_2)/(a_0-a_1)
d = ((a_1**2)-a_0*a_2)/(a_1-a_0)
if r == 1:
    ans = a_0 + 3*d
else:
    ans = ((a_0-d/(1-r))*r**3) + d/(1-r) 
print(round(ans))